Which groups and individuals do you consider "extreme?" If you say George Soros, your argument is automatically invalid... and something tells me that you think extreme left really means anyone who isn't right-wing.
Do you think the teens were somehow against or indifferent to the idea of gun control after seeing their friends killed with an AR-15, but were manipulated by progressive groups planting 'evil' concepts in their heads, like logic, compassion and a rejection of gun industry bribery?
There was still an outcry during the Obama administration. The difference, I'd say, was that having a Democratic President meant there was a powerful voice for reasonable gun control at the highest levels of power. In the Trump era, where the gun industry has a stranglehold on power, the public has the loudest voice.
And please don't trot out the "guns weren't the cause" crap. That's not what we're arguing. It's that certain kinds of guns enable violence on a large scale, and have no good uses for self-defense or hunting. The Parkland killer took 17 lives in the space of 6 minutes and 20 seconds. The Las Vegas shooter killed 58 people and injured hundreds more in the space of about 10 minutes. It's difficult to completely avoid mass shootings so long as guns are readily available, but there would be considerably more survivors of those incidents if the attackers had been forced to use handguns or bolt-action rifles.